Transmissions with continuously variable gear ratios (CVT) using variators in the form of two electric machines, each one of which being capable to operate either as a generator or as a motor, are well known and are used in some hybrid car models available on the market today in which the electric machines are used alone or in parallel with the combustion engine as a driving power source. Common to these hybrid cars available on the market is that one of the electric machines is always linked to the transmission output shaft and hence its speed is coupled to the speed of the vehicle over the whole speed range, that is even in the high speed range.
The driveability, performance and fuel economy of a hybrid car can be improved if the above described “single mode” operated electromechanical CVT were to be replaced with a transmission of the present invention which has two modes of operation. In low mode, i.e. reverse driving, standstill with engine running and forward driving in low speed, e.g. below 50 km/h, the transmission is controlled so that the variator (electric machines) delivers torque via a separate gear train to the output side of the transmission, thereby by-passing the planetary gear train, while the combustion engine torque is transmitted via the planetary gear train. In high mode which is for driving in higher speeds the transmission is controlled so that both the engine and the variator deliver torque via the planetary gear train. In this manner each gear train can be optimized for a certain speed range.
However, due to packaging requirements due to the size of the electric machines required, among other things, cars equipped with a two mode CVT using two electric machines as a variator have not yet been commercially available.